At present isophorone diisocyanate, IPDI, is the commonly used isocyanate curative for hydroxyterminated polymers used in the rocket propellant industry. An alternate curing agent that has the desirable properties of IPDI has been sought because IPDI is foreign made. IPDI cannot at this time be produced in this country because of international patent rights and environmental constraints; therefore; in case of national crisis, it might become unavailable.
As noted hereinabove, isophorone diisocyanate, IPDI, has environmental constraints against being produced in this country since it is made by a phosgenation process. Although the current supply at the price from the foreign source, (e.g., of about $3.00 per pound), is a preferred price to that which could be met, if it could be produced in this country, with all things considered, it is prudent in case of national crisis to not be restricted to a foreign source which might become unavailable.
An alternate curing agent meta-tetramethylxylene diisocyanate (m-TMXDI) would offer advantages which the presently used IPDI could not meet in this country. The domestically produced m-TMXDI is made by a non-phosgenation process developed by American Cyanamid Company's research laboratories. The applications of m-TMXDI and p-TMXDI in reaction injection molding (RIM) permits the manufacture of urethane parts which require no post-painting. The isomers of either TMXDI which are naturally white (or can be pigmented any desired color) are light stable; and if scratched or damaged in use, they retain their integral color. The introduction of a new family of aliphatic diisocyanates to the polyurethane industry provides the products which motivates further research in another industry, i.e., the propulsion industry, to meet a current need.
Composite rocket propellants that are cured and crosslinked with a domestically produced acceptable substitute for IPDI is presently needed. An acceptable substitute for crosslinking hydroxyterminated polymers of polybutadiene binders employed in composite rocket propellants would be highly desirable if, additionally, improved propellant properties are derived from its use.